(1) Field of the Invention
The invention relates to a therapy system for irradiating a target volume within a patient with a charged particle beam, comprising                a charged particle beam generator,        a beam transport system for transporting the charged particle beam,        a nozzle for delivering the charged particle beam to the target volume,        an X-Ray device comprising an X-Ray source for emitting X-Rays towards the target volume, the X-Ray device being movably mounted into the nozzle between a first position wherein the X-Ray device is inside of a treatment path envelope of the charged particle beam within the nozzle and a second position wherein the X-Ray device is outside of said treatment path envelope,        an X-Ray receiving device mounted opposite to the patient with regard to the X-Ray source, and in optical alignment with the X-Ray source when the X-Ray device is in the first position,        
(2) Description of Related Art
Such therapy systems are known from international patent application number PCT/US97/19236, published under international publication number WO98/18523.
In such known therapy systems, an X-Ray device including an X-Ray source, for example an X-ray tube, is movably mounted inside the nozzle between aforementioned two positions. When the X-Ray device is in its first position, the X-Ray source is able to emit X-Rays towards the X-Ray receiving device for generating an X-Ray image of the target volume. Given the position and orientation of the X-Ray source within the nozzle, such image is often called a beam-eye view (BEV) image of the target volume. Such image is used to determine if the target volume is correctly aligned with regard to the charged particle beam path and eventually to modify a spatial position of the patient in order to obtain such correct alignment. When the alignment is correct, the X-Ray device is moved away to its second position so as to leave the path free to the charged particle beam for irradiating the target volume. These basic principles are well known in the art and will therefore not be detailed further.
Of interest here is that, in such known therapy systems, the X-Ray device is moveable between aforementioned two positions following a translatory movement within the nozzle. To this end, international patent application number PCT/US97/19236 discloses for example an X-Ray device comprising an X-Ray source which is mounted on a sled which is moveable along two parallel guiding tracks and a screw motor assembly which is operatively connected to the sled for moving the X-Ray device along the guiding tracks between its two positions.
Although such known systems work well, they require a relatively complex and hence expensive mechanical assembly for moving the X-Ray device. They also set a relatively important stroke on the X-Ray device, which in turn requires particular means for bringing electrical power and cooling fluid to the X-Ray device.
Furthermore, for nozzles applying beam scanning methods for obtaining a conformal irradiation of the target volume, such as pencil beam scanning methods, it is desirable that a certain degree of vacuum is created inside the nozzle in order to reduce scattering effects on the particle beam while it travels within the nozzle. This is particularly true for pencil beam scanning methods where small beam spots are required at an isocenter of the system, such as beam spots having a size between 2 mm and 10 mm.
Now, many of the standard mechanical components which are being used for moving the X-Ray device in the known systems are not suited for operating in a vacuum and would therefore have to be redesigned and/or reengineered for operation in such an environment. This would in turn increase the complexity, the costs, and most probably the weight and the bulk of the system.